The goal of this project is to investigate the molecular mechanisms underlying the malignant transformation of cells. In our studies, we have made use of a RNA tumor virus (human T- lymphotropic virus type 1) and a DNA tumor virus (human adenovirus type 12). We have succeeded in deriving transgenic mouse models for the study of neurofibromatosis, gastric carcinoma, and mammary carcinoma. These experimental models will be particularly useful not only for improved diagnosis and treatment of the corresponding human malignancy, but also for a detailed analysis of the molecular basis for their etiology.